Water-in-oil emulsion explosives are well-known in the art. See, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives are found to have certain advantages over conventional aqueous slurry explosives, which have a continuous aqueous phase, as described in U.S. Pat. No. 4,141,767.
An inherent problem with emulsion explosives, however, is their relative instability, due to the fact that they comprise a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable, these supercooled droplets are prevented from crystallizing or solidifying into a lower energy state. If the emulsion weakens or becomes unstable, however, then crystallization or solidification of the droplets results, and the explosive generally loses at least some of its sensitivity to detonation and becomes too viscous to handle for certain blasting applications. Moreover, it is common to add solid components to emulsion explosives, such as glass microspheres for density reduction and prills or particles of oxidizer salt such as porous prilled ammonium nitrate (AN) for increased energy. These solid components, however, tend to destabilize emulsions.
Emulsion explosives commonly are used as a repumpable explosive, i.e., an explosive that is formulated at a remote facility, loaded or pumped into a bulk container and then transported in the container to a blasting site where it then is "repumped" from the container into a borehole. Alternatively, the explosive may be delivered (repumped) into a centrally located storage tank from which it will be further repumped into a vehicle for transportation to a blasting site and then again repumped into the borehole. Thus the emulsion explosive must remain stable even after being subjected to repeated handling or shearing action, which normally also tends to destabilize an emulsion. Additionally, the emulsion's viscosity must remain low enough to allow for repumping at reasonable pressures and at the low ambient temperatures that may be experienced during colder months. Repeated handling or shearing action also tends to increase the emulsion's viscosity.
Since a density control agent is required in many instances to reduce the density of an explosive and thereby increase its sensitivity to a required level for detonation, and since hollow microspheres are a preferred form of density control, it is important that the emulsion remain stable and have a low viscosity even when containing solid density control agents.
U.S. Pat. No. 4,708,753 discloses water-in-oil emulsions containing as the emulsifier a salt derived from a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or amide derivative thereof, and an amine. The bis-substituted derivative, nonionic emulsifiers of the present invention differ from these prior art emulsifiers which are anionic mono-substituted derivatives.
U.S. Pat. No. 4,615,751 discloses the use of an unspecified polybutenyl succinic anhydride derivative (with a tradename of EXPERSE 60) as a water-resisting agent in emulsions containing prills but not as an emulsifier. European Patent Application No. 0 155 800 discloses alkanolamine derivatives of polyisobutenyl succinic anhydride as emulsifiers but the examples all contain mono-derivatives, the vast majority of which have higher chain lengths than those of the present invention. In fact, 1:1 alkanolamine:polyisobutenyl succinic anhydride derivatives are easier to prepare than 2:1 derivatives of the present invention. The teachings in the European Patent Application No. 0 155 800 gravitate toward in-situ emulsifier formation under mild conditions where 1:1 rather than 2:1 derivatives of hydrophobic moities and polyisobutenyl succinic anhydride are favored.
U.S. Pat. No. 4,710,248 discloses water-in-oil emulsion explosives containing as an emulsifier underivatized polyisobutenyl succinic anhydride or polyisobutenyl succinic acid, which differ from the bis- derivatives of the present invention by the lack of substitution on the carboxylate functionality.
U.S. Pat. No. 4,357,184 discloses water-in-oil emulsions containing graft block or branched polymer emulsifiers. One type of block copolymer which is taught contains polyisobutenyl succinic anhydride as the hydrophobic block and polyethylene glycol or polyethylenimine as the hydrophilic block. Block copolymers are clearly distinguishable from the present invention, which involves derivatization of bis carboxylated olefinic or vinyl addition polymers by non-polymeric alkanolamines or polyols. Furthermore, the olefinic chain of the disclosed block copolymer is specified as being from 40 to 500 carbon atoms which is much longer than the chain length of the present invention.
International Publication No. (PCT) WO 88 03522 discloses a polyamine derivative of polyisobutenyl succinic anhydride as an emulsifier, which differs from the monomeric bis- derivatives of the present invention.
As more fully set forth below, the alkanolamine or polyol, nonionic, bis- derivative emulsifier of the present invention offers distinct advantages over all of these prior art emulsifiers.